Field of the Invention
The invention lies in the automotive arts. Specifically, the invention pertains to a method and a corresponding circuit for controlling the braking process in a motor vehicle.
State of the art braking systems with the anti-lock brake feature (e.g. European patent EP 0 644 836 B1) control the brake pressure of the individual wheels of a motor vehicle in such a way that the wheels are prevented from locking during braking. The steerability of the motor vehicle is thus maintained in that the wheel brake pressure is adapted to the respective frictional adhesion of the tire to the road surface. That adaptation is carried out by virtue of the fact that when unacceptably high slip occurs the brake pressure which acts on the individual wheels is reduced and increased again intermittently, and thus discontinuously, using brake pressure control valves.
New requirements that are being made of braking functions and which improve the safety and comfort of the operation of motor vehicles, for example anti-lock brake systems, driving stability systems, traction controllers, "intelligent" driving speed controllers, have led, together with the requirement for a reduction in the assembly and maintenance costs, to the development of new, electrically controlled and actuated brake systems. See, for instance, German published patent application DE 195 29 664. Those systems greatly reduce, or entirely remove, the need for the considerable expenditure on master brake cylinders, brake pressure lines etc. in conventional brake systems.
In such an electric brake system, which is referred to as a brake by wire system, the driver is disconnected from the brake in terms of force, i.e. the braking torque request which the driver makes is no longer transferred directly as force on a hydraulic system but rather now merely an electrical signal is transmitted on an electrical line. The signal thus controls an electric brake actuator. The brake actuator is supplied with electrical energy and generates a frictional force at the individual wheel brakes, by means of which force a braking torque is built up at the respective wheel.